A premixed combustion method is used in the present day combustors a from a standpoint of environmental protection, because, the premixed combustion method achieves a reduction of thermal NOx. The premixed combustion method includes premixing a fuel and excessive air and burning the fuel. In the premixed combustion method it is possible to easily reduce NOx, because the fuel burns under a lean condition in all areas in the combustor. The premixing combustor that employs the premixed combustion method is explained below.
FIG. 13 is a cross-sectional view of the premixing combustor. A pilot cone 610 for forming diffusion flame is provided in a casing 700 of a combustor nozzle block. A fuel nozzle block 29 is fitted to the outlet of the combustor nozzle block casing 700, and this fuel nozzle block 29 is inserted in the liner 19 of a combustion chamber. The pilot cone 610 forms the diffusion flame by allowing a pilot fuel supplied from a pilot fuel supply nozzle (not shown) to react with combustion air supplied from a compressor.
Eight premixed flame forming nozzles 510 are provided around the pilot cone 610 although only one premixed flame forming nozzles 510 is seen in FIG. 13. The premixed gas is produced by mixing combustion air and a main fuel, and is injected from the premixed flame forming nozzles 510 toward the combustor. The premixed gas injected from the premixed flame forming nozzles 510 to the combustor is ignited by a high temperature combustion gas exhausted from the diffusion flame, to thereby form premixed gas combustion flame. High temperature and high pressure combustion gas is exhausted from the premixed gas flame, and the combustion gas is guided to a first stage nozzle of a turbine, through a combustor tail pipe (not shown).
When sudden combustion occurs near the wall surface of the liner of the combustion chamber, oscillating combustion occurs. Conventionally, there is a problem in that combustion becomes unstable due to the oscillating combustion, and hence stable operation cannot be carried out. Further, there is another problem in that when combustion occurs near the wall surface of the liner of the combustion chamber, the liner of the combustion chamber is overheated, thereby shortening the life thereof. When the life of the liner of the combustion chamber becomes short, repair and replacement are required frequently, and hence time and energy are required for maintenance.
It is an object of the present invention to solve at least the problems in the conventional technology.